// part1:C14:ex14.6.cpp
// class Sales_data.
#include <iostream>
class Sales_data
{
    friend ostream& operator<<(ostream &os, const Sales_data &item)
    {
        const char *sep = ' ';
        os << item.isbn() << sep << item.units_sold << sep <<
            item.revenue << sep << item.avg_price();
        return os;
    }
};
